I think generally Thug/SC tend to be concerned specifically with melee. The sniper/artillery builds seem to be less universally useful. Like in your example, since they're indie mages, you can't count on ever having them. Also, you probably won't give them any gear but the ranged item and a couple specific boosters (eye/boots), but much less gems invested than most melee units would expect.
I'm a little confused by the chart though, so not sure what else to add.
